| 摘要 |
PURPOSE:To correct variation of an image plane represented as short-distance variation in aberration, specially, variation in astigmatism by using the 1st lens group for focusing and also moving lens groups from the 1st group to an object-side lens group at an afocal group interval along an optical axis. CONSTITUTION:Light is parallel luminous flux between the 3rd and the 4th lens groups G3 and G4 in an infinite-distance focusing state and a focal part is constituted. The 1st lens group G1 is moved toward the object side by distance DELTAXF for focusing on a short-distance body P, and then lens groups G1, G2, and G3 are moved toward the object side by distance DELTAx. This movement extent is stored in a storage element to perform microcomputer control. Thus, astigmatism is compensated excellently without exerting any influence upon spherical aberration. |
